Multifunctional nanoparticles to improve treatment of human glioblastoma The long-term objective of this research is to develop novel therapeutic approaches to improve the clinical outcome of adult patients with glioblastoma multiforme (GBM), the most common and lethal human primary brain tumor. Recent clinical trials have demonstrated that administration of the methylating agent temozolomide (TMZ) during post-operative therapy significantly increases survival of GBM patients. Although TMZ in combination with radiation is now the contemporary standard of care for GBMs, the majority of GBMs are not responsive due to the resistance mediated by O6-methylguanine-DNA methyltransferase (MGMT), a DNA repair protein that limits the radiosensitizing and cytotoxic effects of TMZ. Recent studies from our group and others suggest that the resistance of GBMs to TMZ can be overcome by ablating MGMT activity with DNA repair inhibitors. However, the clinical utility of DNA repair inhibitors have been hindered by their poor pharmacokinetics such as poor permeability of the blood-brain barrier (BBB), a short half-life, and bone marrow producing deleterious side-effects. We propose to develop a multifunctional nanoparticle (NP) that can deliver DNA inhibitors specifically to GBM cells to circumvent treatment-resistance and treatment-limiting systemic toxicity. Our multidisciplinary team has developed prototype NPs consisting of an iron oxide core surrounded by a shell of a biodegradable polymer of polyethylene glycol grafted chitosan (PEG-chitosan). The core-shell structure is conjugated with the near-infrared fluorophore Cy5.5 and the targeting ligand chlorotoxin (CTX). Each element of this NP system confers a property that makes it an excellent candidate as an image-guided drug delivery vehicle. In this study, inhibitors are covalently attached to the outer shell of the NP tht is crosslinked by disulfide linkage and can be rapidly degraded by glutathione-mediated reduction in cytosol of target cells to release the payload but not in blood. The project includes the following Specific Aims: (1) Fabrication and characterization of inhibitor derivatized NPs; (2) Assessment of therapeutic effects of NPs on human GBM cells, and in vivo toxicity and BBB permeation of NPs; (3) Study of therapeutic efficacy of NPs in an orthotopic GBM xenograft model of human GBM. Our NPs incorporate features that facilitate drug loading, protect drug during transport, penetrate the BBB, facilitate rapid intracellular release, and confer tumor specificity. Moreover, each component material of the NP is biocompatible and assumes multiple functions. This strategy combines the advances in forefront research of GBM cancer biology with advanced nanotechnology in tumor imaging and therapeutics to circumvent the resistance to treatment. Successful completion of the proposed work may produce a novel therapeutic agent that can be readily brought to clinical trial as our NP is expressly designed to improve the efficacy of the current standard of care for GBM. The expanded health relevance of this research is that the NPs with BBB penetration ability may also facilitate the delivery of therapeutic agents to brain metastases from a variety of tumors.